1. Field of Invention
The invention relates to a seawater filter and, in particular, to a device that filters seawater centrifugally.
2. Related Art
Please refer to FIG. 6 for a conventional seawater filter 8. A water supply pump 81 draws seawater to a pre-filter 82 to filter out impurities in larger sizes. The seawater is then transmitted to a post-filter 83 that can filter out smaller impurities. Afterwards, a pressurizing pump 84 transports the filtered seawater to a reverse osmosis (RO) system 85 to turn it into fresh water.
Although the above-mentioned seawater filter can desalinate seawater into fresh water, large and small impurities accumulate on the filtering materials of the filters 81, 82 during the desalination process. One then has to frequently replace the filtering materials to avoid clogging. The high cost for filtering materials is thus a primary problem.
Please refer to FIG. 7 for another conventional seawater filter 91. It involves a heating unit 911, a desalinating unit 912, and a purifying and distilling unit 913 working repeatedly and cyclically. Through multiple desalination steps of a separating and reducing device (not shown) in the desalinating unit 912 and multiple filtering and purifying processes of a distiller (not shown) in the purifying and distilling unit 913, components in seawater are decomposed to the tiniest particles, thereby achieving the desalinating, filtering, and purifying effects.
However, such a seawater filter requires the use of the heating unit 911. The purifying and distilling unit 913 then collects water vapor. In this case, the overall cost of the device is the primary problem.
Please refer to FIG. 8 for yet another conventional seawater filter 92. Several connected desalinating layers 922 are disposed inside a centrifugal cylinder 921. Each of the desalinating layers 922 includes a stainless steel cathode, a graphite anode, and an electrode screen. Seawater is injected via the top water inlet of the centrifugal cylinder 921. The stainless steel cathode and the graphite anode throw out objects adhering thereon as they rotate. Through the effects of an electric field and centrifugal force, seawater passes through each of the desalinating layers 922 in the centrifugal cylinder 921. Each layer has an electric field produced by the electrodes and a centrifugal force produced by rotation. Therefore, all the positively charged ions in seawater move towards the cathode, while all the negatively charged ions move towards the anode. The electrode screen filters the ions, so that the positively and negatively charged ions in seawater are reduced. Eventually, the seawater is desalinated to fresh water.
However, such a conventional seawater filter has to have the components of stainless steel cathodes, graphite anodes, and electrode screens. The electric field is generated by an electric field. Thus, it has even higher device and operating costs than the previously mentioned two conventional seawater filters.